Femoral Head Allograft for Large Talar Defects Using a Lateral Approach

Talar body avascular necrosis with collapse or infection (FIG 1A) is one indication for femoral head allograft.

Failed total ankle arthroplasty with insufficient bone remaining for revision (FIG 1B) also warrants a femoral head allograft.

Use of a femoral head graft for those patients with severe (>25 degrees) hindfoot valgus may not be appropriate because correction of the deformity can cause significant lateral soft tissue tension and lead to tissue necrosis and poor wound healing. In those cases, a tibiocalcaneal fusion with shortening of the medial ankle may be more appropriate.

POSITIONING

Under a general or spinal anesthetic block, the patient is placed in a supine position on the operating table with the ipsilateral hip bumped to facilitate internal rotation of the leg.

The lower extremity is prepped and draped in the usual fashion, and a thigh tourniquet inflated to 250 mm Hg is applied after exsanguination of the leg with an Esmarch bandage.

TECHNIQUES

Preparation for Allograft

A 12- to 14-cm lateral incision is made along the distal fibula, starting 6 cm above the ankle joint and extending distally along the anterior border of the peroneal tendons to the peroneal tubercle (TECH FIG 1A).

The tendons are carefully retracted posteriorly to expose the distal fibula, lateral ankle, and subtalar joints.

The fibula is osteotomized 6 cm above the joint (or as high as necessary to allow placement of the locking plate on the tibia) then excised and morcelized for later grafting (TECH FIG 1B).

Débridement of avascular bone and removal of osteophytes or implant is performed until only viable bone surfaces remain (ie, distal tibial plafond, talar head and neck, and posterior facet of the subtalar joint).

Determine the size of acetabular reamer from the total hip arthroplasty set that best fits the defect (TECH FIG 1C).

Only enough subchondral bone is removed from the tibia, talar neck, and calcaneus to expose viable, softer cancellous bone for fusion to the femoral head graft.

If an assistant holds the foot and ankle in the desired position, the surgeon can ream the defect safely, without the ankle bouncing around.

No provisional fixation is necessary: The ankle is still relatively stable even after the ankle implant or necrotic bone is removed.

With the ankle and hindfoot held in neutral, the defect is reamed (TECH FIG 1D). The desired position of fusion is with the ankle in neutral plantar/dorsiflexion flexion and the hindfoot in approximately 5 degrees of valgus in relation to the distal tibia.

It is critical to protect the soft tissue about the ankle with either Army-Navy or Hohmann retractors while the acetabular reamers are used.

Bone shavings are saved and mixed with the morcelized fibular graft.

Preparation and Placement of Allograft

An allograft femoral head is thawed in a warm saline bath at the beginning of the procedure and placed in the bone vice (Allogrip Bone Vise, DePuy, Warsaw, IN), with the three limbs of the vice gripping the femoral neck.

The female reamer corresponding to the same size male reamer used for reaming the defect is used to decorticate the allograft.

It is optimal to ream only 2 or 3 mm of bone from the head to avoid significantly weakening the compressive strength of the graft (TECH FIG 2A–C).

The head can be drilled multiple times in areas that still contain hard sclerotic bone to facilitate fusion.

The appropriately sized and decorticated femoral head allograft is then placed in the defect (TECH FIG 2D).

Ankle and foot position is then checked for neutral position (ie, neutral ankle dorsiflexion–plantarflexion, 5 degrees of hindfoot valgus, and neutral rotation of the foot on the tibia). Because the femoral head graft is spherical, it is relatively easy to dial in the correct position of the ankle and hindfoot.

The femoral neck is marked flush with the lateral tibia, the graft is removed, and the femoral neck is cut with a large oscillating saw.

A bone slurry graft, made up of the autograft from the fibula and male reamers, is then placed in the defect to fill any voids around the fusion site (TECH FIG 2E).

The male reamers can again be placed and used in reverse to evenly spread the graft.

The femoral head graft is placed back in the defect, and alignment is checked to ensure that it sits flush with the lateral fusion surface.

Again, no provisional fixation is needed, as the interference fit between the femoral head and the recipient site is very stable.

This will allow unimpeded placement of the lateral blade plate.

Placement of Plate and Screws

The 90-degree blade plate is then sized by placing it along the lateral fusion surface equidistant between the anterior and posterior surfaces of the tibia and femoral head graft.

In my experience, fixation with six to eight cortical screws in the tibia proximal to the femoral head allograft is desirable; therefore, a blade plate of appropriate length is required. The decision depends on the quality of bone.

Typically, for six cortical screws to be positioned in the tibia above the graft, a nine-hole blade plate will be needed.

The distal end of the plate (the blade end) should line up with the center of the calcaneal body to ensure maximum hold and minimize the chance of fracturing the calcaneus with insertion.

Usually, a six- to eight-hole plate with the short blade fits well.

Once the plate size has been selected, place the plate “backward” along the lateral fusion area so the blade is pointing lateral (TECH FIG 3A). This technique allows for proper angle of insertion of the guidewire and, therefore, the blade of the plate.